1) Field of the Invention
The present invention relates to an information recording/reproducing apparatus for use in an optical card, in which the optical card is arranged to be moved in a reciprocal manner with respect to an optical head arranged in the apparatus. Particularly, the apparatus according to the invention is arranged such that information data can be read out in a stable manner even when the moving speed of the optical card is varied.
2) Related Art Statement
An optical card, which is not rewritable, has a large memory storage and is very convenient for carrying. Therefore, such an optical card is widely applied as a private health management card, a portable map, a bankbook, or a prepaid card for shopping.
Such an optical card has a construction as shown in FIG. 1. On the optical card, a plurality of data tracks are pre-recorded in a longitudinal direction of the optical card; and optical information is recorded/reproduced by relatively moving the optical card and the optical head in the track direction and in a direction perpendicular thereto. Optical information is modulated under a self-clock system modulation method, such as MFM modulation method, to be recorded on the optical card. When reproducing optical information recorded on the optical card, synchronous clock pulses are extracted from read out signals by a PLL method, and information data is reproduced based on the thus extracted synchronous clock pulses.
In Japanese Patent Laid-open Preliminary Publication No. 2-282973, an information recording/reproducing apparatus, which is arranged such that the optical card is held in a shuttle and the shuttle is driven with the aid of a VCM (voice coil motor), is disclosed.
Further, in Japanese Patent Laid-open Preliminary Publication No. 63-25868, another information recording/reproducing apparatus, in which a variation of moving speed of the shuttle holding an optical card therein is detected by using an encoder, and the read out signals are corrected by the thus detected variation of moving speed of the shuttle, is disclosed.
Generally, in an optical information recording/reproducing apparatus for an optical disc, a variation of rotation of the disc is very small because the optical disc per se has an inertia; and therefore, the variation of the rotation of the disc does not affect the synchronous clock pulses so much. However, in the optical information recording/reproducing apparatus for an optical card, it is necessary to move the optical card linearly with respect to the optical head in a reciprocal manner. Therefore, it is impossible to utilize the inertia to remove the variation of the moving speed of the optical card, so that the variation of the moving speed of the optical card becomes large.
In the apparatus disclosed in Japanese Patent Preliminary Publication No. 2-282973, the voice coil motor is used to drive the shuttle holding the optical card therein in order to restrain the variation of the moving speed of the optical card. By the voice coil motor it is possible to drive the shuttle without a driving mechanism such as a gear, and the voice coil motor has an excellent controllability. Therefore, the variation can be restrained to be extremely small. Further, in the apparatus disclosed in Japanese Patent Preliminary Publication No. 63-25868, the read out signal is corrected on the basis of a signal detected by the encoder, which is arranged on the shuttle, in order to absorb the variation of moving speed of the optical card.
However, when relatively driving the optical card with respect to the optical head in a reciprocal manner, the optical card should be stopped at both end portions of its moving area. Further, a distance from both the end portions to the information recording/reproducing area, within which the moving speed of the optical card should be increased up to a normal speed, is very short, i.e. about 5 mm. Therefore, in case of controlling the movement of the shuttle by using the voice coil motor, it is required that the voice coil motor have a large thrust. As a result, the cost for manufacturing the apparatus becomes expensive, the size of apparatus becomes large, and the weight becomes heavy.
On the other hand, in case of detecting the moving speed of the shuttle by using an encoder, the cost for manufacturing becomes expensive too, because of the price of the encoder. Further, when correcting the read out signal on the basis of the signal detected by the encoder, an encoder having a fine pitch is required, because it is necessary to detect the moving speed of the shuttle with a high accuracy. Therefore, the cost therefor becomes high. If an encoder having a rough pitch is used, such encoder could not follow any sudden change of the moving speed of the shuttle, so that information data could not be read out correctly.